Various strategies are known for increasing the amount of power that a gas turbine engine may be able to produce. One method of increasing the power output of a gas turbine engine is by cooling the inlet air before compressing it in the compressor. Such inlet cooling causes the air to have a higher density so as to create a higher mass flow rate into the compressor. The higher mass flow rate of the air in a compressor allows more air to be compressed so as to allow the gas turbine engine to produce more power.
One type of cooling system involves latent or evaporative cooling. Such a system uses water at ambient temperature to cool the air by dropping the air temperature due to water evaporation. One example of such a system is a media-based evaporative cooler that operates by running water over plates or over a cellular media inside of a chamber and then drawing the air through the chamber to evaporate the water. Another example of an evaporative cooling system utilizes a high-pressure nozzle spray system to spray water into the air for evaporation. Evaporative cooling can cool the incoming air to near its wet bulb temperature. Evaporative cooling can be an efficient method of cooling the inlet air because there is only a minimal amount of parasitic power that is required to run the evaporative cooling system as compared to other types of inlet cooling system such as coil cooling systems and the like.
Another power augmentation method is the use of wet compression. Wet compression generally involves spraying water droplets into the inlet of the compressor. When the mixture of gas and water is compressed, the temperature of the gas increases and provides the driving potential for evaporation. The evaporation of the water cools the gas and, hence, increases the available power by reducing the work required for compression.
Issues with known evaporative cooling systems may include flow resistance pertaining to a media-type evaporative cooler. The typical pressure drop caused by the media-type evaporative cooler to the gas turbine inlet airflow may be in the range of about 0.25 to about 0.75 inches water column (about 0.635 to about 1.9 centimeters). Other issues with evaporative cooling and wet compression include high nozzle abrasion rates found in water spray evaporative cooling systems, i.e., high nozzle abrasion rates caused by the high speed jet flows through the spray nozzles. Another problem is the requirement of costly high pressure water supply systems to supply high-pressure evaporative cooling and wet compression spray systems. Further, there is also the risk of unevaporated large water droplets from evaporative cooling or wet compression systems entering the compressor and causing erosion or other damage to the compressor blades.
There is thus a desire for an improved gas turbine inlet evaporative cooling system as well as a wet compression system. Such systems may reduce the pressure drop thereacross, eliminate or avoid nozzle abrasion, utilize standard low pressure water supply systems, and prevent downstream damage to the compressor blades by unevaporated large water droplets. Moreover, such systems should provide power augmentation without being a significant parasitic power loss on the gas turbine engine as a whole. The gains of power augmentation are less limited by the high ambient relative humidity conditions than those found in the gas turbines using only media-type evaporative cooling.